The Gnutella2 protocol, often referred to as G2, is, despite its name, not a successor protocol of gnutella, but rather a fork. A sore point with many gnutella developers is that the Gnutella2 name conveys an upgrade or superiority, which led to a Gnutella2 flame war. Other criticism included the use of the gnutella network to bootstrap G2 peers and poor documentation of the G2 protocol. Additionally, the search retries of the Shareaza client, which was one of the initial G2 clients, could unnecessarily burden the gnutella network.
The fork took place in 2002 and both protocols have undergone significant iterations since that time. G2 has advantages and disadvantages compared to gnutella. An advantage often cited is Gnutella2's hybrid search is more efficient than the original gnutella query flooding, which was used in 2002. An advantage for gnutella is its user population numbers in the millions, whereas the G2 network is approximately an order of magnitude smaller. It is difficult to compare the protocols in their current form; the individual client choice will probably have as much an effect to an end user on either network.
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